Geared turbofan with three turbines with first two counter-rotating, and third co-rotating with the second turbine

ABSTRACT

A gas turbine engine has a fan rotor, a first compressor rotor and a second compressor rotor. The second compressor rotor compresses air to a higher pressure than the first compressor rotor. A first turbine rotor drives the second compressor rotor and a second turbine rotor. The second turbine drives the compressor rotor. A fan drive turbine is positioned downstream of the second turbine rotor. The fan drive turbine drives the fan through a gear reduction. The first compressor rotor and second turbine rotor rotate as an intermediate speed spool. The second compressor rotor and first turbine rotor together as a high speed spool, with the high speed spool rotating in an opposed direction to the intermediate speed spool. The fan drive turbine rotates in the same direction as the intermediate speed spool.

BACKGROUND

This application relates to a gas turbine having three turbine sections,with one of the turbine sections driving a fan through a gear changemechanism.

Gas turbine engines are known, and typically include a compressorsection compressing air and delivering the compressed air into acombustion section. The air is mixed with fuel and combusted, and theproduct of that combustion passes downstream over turbine rotors.

In one known gas turbine engine architecture, there are two compressorrotors in the compressor section, and three turbine rotors in theturbine section. A highest pressure turbine rotates a highest pressurecompressor. An intermediate pressure turbine rotates a lower pressurecompressor, and a third turbine section is a fan drive turbine whichdrives the fan.

More recently, a gear reduction has been incorporated between the fandrive turbine and the fan. This allows the fan to operate at a lowerspeed than the turbine.

SUMMARY

In a featured embodiment, a gas turbine engine has a fan rotor, firstand second compressor rotors, with the second compressor rotorcompressing air to a higher pressure than the first compressor rotor. Afirst turbine rotor drives the second compressor rotor and a secondturbine rotor. The second turbine drives the first compressor rotor. Afan drive turbine is positioned downstream of the second turbine rotor,and drives the fan through a gear reduction. The first and secondcompressor rotors rotate as an intermediate speed spool. The secondcompressor rotor and first turbine rotor rotate together as a high speedspool, with the high speed spool rotating in an opposed direction to theintermediate speed spool. The fan drive turbine rotates in the samedirection as the intermediate speed spool.

In another embodiment according to any of the previous embodiment, thefan rotor is driven by the gear reduction to rotate in the samedirection as the high speed spool.

In another embodiment according to any of the previous embodiment, apower density of the engine is greater than or equal to about 1.5lbs/in³, and less than or equal to about 5.5 lbf/in³.

In another embodiment according to any of the previous embodiment, thepower density is defined as a ratio of thrust produced by the engineexpressed in pounds force to a volume of a turbine section incorporatingeach of the first turbine rotor, second turbine rotor and fan driveturbine rotor, expressed in cubic inches.

In another embodiment according to any of the previous embodiment, theratio is greater than or equal to 2.0.

In another embodiment according to any of the previous embodiment, theratio is greater than or equal to about 4.0.

In another embodiment according to any of the previous embodiment, thethrust is sea level take-off flat-rated static thrust.

In another embodiment according to any of the previous embodiment, thefan delivers a portion of air into a bypass duct and into the firstcompressor rotor as core flow.

In another embodiment according to any of the previous embodiment, amid-turbine frame is positioned between the first and second turbinerotors.

In another embodiment according to any of the previous embodiment, aturning vane is positioned between the mid-turbine frame and secondturbine rotor.

In another embodiment according to any of the previous embodiment, avane is positioned between the second turbine rotor and fan driveturbine.

In another embodiment according to any of the previous embodiment, avane is positioned between the second turbine rotor and fan driveturbine.

In another embodiment according to any of the previous embodiment, amid-turbine frame is positioned between the first and second turbinerotors.

In another embodiment according to any of the previous embodiment, aturning vane is positioned between the mid-turbine frame and secondturbine rotor.

In another embodiment according to any of the previous embodiment, avane is positioned between the second turbine rotor and fan driveturbine.

In another embodiment according to any of the previous embodiment, avane is positioned between the second turbine rotor and fan driveturbine.

In another featured embodiment, a gas turbine engine has a fan rotor,first and second compressor rotors, with the second compressor rotorcompressing air to a higher pressure than the first compressor rotor. Afirst turbine rotor drives the second compressor rotor, and a secondturbine rotor, with the second turbine driving the first compressorrotor. A fan drive turbine is positioned downstream of the secondturbine rotor. The fan drive turbine drives the fan through a gearreduction. The first compressor rotor and second turbine rotor rotate asan intermediate speed spool. The second compressor rotor and firstturbine rotor rotate together as a high speed spool rotating in anopposed direction to the intermediate speed spool. The fan drive turbinerotates in the same direction as the intermediate speed spool. The fanrotor is driven by the speed reduction to rotate in the same directionas the high speed spool. A power density of the engine is greater thanor equal to about 1.5 lbf/in³, and less than or equal to about 5.5lbf/in³. The power density is defined as a ratio of thrust produced bythe engine expressed in pounds force to a volume of a turbine sectionincorporating each of the first turbine rotor, second turbine rotor andfan driving turbine rotor, expressed in cubic inches.

In another embodiment according to any of the previous embodiment, theratio is greater than or equal to 2.0.

In another embodiment according to any of the previous embodiment, theratio is greater than or equal to about 4.0.

In another embodiment according to any of the previous embodiment, thethrust is sea level take-off flat-rated static thrust.

These and other features of the invention would be better understoodfrom the following specifications and drawings, the following of whichis a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a gas turbine engine.

FIG. 2 shows how a volume of the turbine section can be calculated.

DETAILED DESCRIPTION

A gas turbine engine 20 is illustrated in FIG. 1, and incorporates a fan22 driven through a gear reduction 24. The gear reduction 24 is drivenwith a low speed spool 25 by a fan/gear drive turbine (“FGDT”) 26. Airis delivered from the fan as bypass air B, and into a low pressurecompressor 30 as core air C. The air compressed by the low pressurecompressor 30 passes downstream into a high pressure compressor 36, andthen into a combustion section 28. From the combustion section 28, gasespass across a high pressure turbine 40, low pressure turbine 34, andfan/gear drive turbine 26.

A plurality of vanes and stators 50 may be mounted between the severalturbine sections. In particular, as shown, the low pressure compressor30 rotates with an intermediate pressure spool 32 and the turbine 34 ina first (“−”) direction. The fan drive turbine 26 rotates with a shaft25 in the same (“−”) direction as the low pressure spool 32. The speedchange gear 24 may cause the fan 22 to rotate in an opposed, second(“+”) direction. However, the fan rotating in the same direction (thefirst direction) would come within the scope of this invention. As isknown within the art, a star gear arrangement may be utilized for thefan to rotate in the same direction as to the fan/gear drive turbine 26.On the other hand, a planetary gear arrangement may be utilized in theillustrated embodiment, wherein the two rotate in opposed directions.The high pressure compressor 36 rotates with a spool 38 and is driven bya high pressure turbine 40 in a direction (“+”) opposed to the spool 32and shaft 25.

Since the turbine 34 and 26 are rotating in the same direction, a firsttype of vane 42 is incorporated between these two sections. On the otherhand, since the high pressure turbine 40 and low pressure turbine 34 arerotating in opposed directions, an air turning vane 50 (such as an airturning mid-turbine frame (“tmtf”) vane) may be positioned between thesetwo sections. The turning vane 50 may be incorporated into a mid-turbineframe which also provides a support for the high pressure turbine rotor40.

The fan drive turbine 26 in this arrangement can operate at a higherspeed than other fan drive turbine arrangements. The fan drive turbinecan have shrouded blades, which provides design freedom.

The low pressure compressor may have more than three stages. The fandrive turbine has at least three, and up to six stages. The highpressure turbine as illustrated may have one stage, and the low pressureturbine may have one or two stages.

The above features achieve a more compact turbine section volumerelative to the prior art, including both the high and low pressureturbines. A range of materials can be selected. As one example, byvarying the materials for forming the low pressure turbine, the volumecan be reduced through the use of more expensive and more exoticengineered materials, or alternatively, lower priced materials can beutilized. In three exemplary embodiments the first rotating blade of thefan drive turbine can be a directionally solidified casting blade, asingle crystal casting blade or a hollow, internally cooled blade. Allthree embodiments will change the turbine volume to be dramaticallysmaller than the prior art by increasing low pressure turbine speed.

Due to the compact turbine section, a power density, which may bedefined as thrust in pounds force produced divided by the volume of theentire turbine section, may be optimized. The volume of the turbinesection may be defined by an inlet of a first turbine vane in the highpressure turbine to the exit of the last rotating airfoil in thefan/gear drive turbine 26, and may be expressed in cubic inches. Thestatic thrust at the engine's flat rated Sea Level Takeoff conditiondivided by a turbine section volume is defined as power density. The sealevel take-off flat-rated static thrust may be defined in pounds force,while the volume may be the volume from the annular inlet of the firstturbine vane in the high pressure turbine to the annular exit of thedownstream end of the last rotor section in the fan drive turbine. Themaximum thrust may be sea level take-off thrust “SLTO thrust” which iscommonly defined as the flat-rated static thrust produced by theturbofan at sea-level.

The volume V of the turbine section may be best understood from FIG. 2.The volume V is illustrated by dashed line, and extends from an innerperiphery I to an outer periphery O. The inner periphery is somewhatdefined by the flowpath of the rotors, but also by the inner platformflow paths of vanes. The outer periphery is defined by the stator vanesand outer air seal structures along the flowpath. The volume extendsfrom a most upstream 400 end of the most upstream blade 410 in turbinesection 40, typically its leading edge, and to the most downstream edge401 of the last rotating airfoil 412 in the fan drive turbine section26. Typically, this will be the trailing edge of that airfoil.

The power density in the disclosed gas turbine engine is much higherthan in the prior art. Eight exemplary engines are shown below whichincorporate turbine sections and overall engine drive systems andarchitectures as set forth in this application, and can be found inTable I as follows:

TABLE 1 Thrust Thrust/turbine SLTO Turbine section volume from sectionvolume Engine (lbf) the Inlet (lbf/in³) 1 17,000 3,859 4.4 2 23,3005,330 4.37 3 29,500 6,745 4.37 4 33,000 6,745 4.84 5 96,500 31,086 3.1 696,500 62,172 1.55 7 96,500 46,629 2.07 8 37,098 6,745 5.50

Thus, in embodiments, the power density would be greater than or equalto about 1.5 lbf/in̂3. More narrowly, the power density would be greaterthan or equal to about 2.0 lbf/in̂3.

Even more narrowly, the power density would be greater than or equal toabout 3.0 lbf/in³.

More narrowly, the power density is greater than or equal to about 4.0lbf/in³.

Also, in embodiments, the power density is less than or equal to about5.5 lbf/in³.

The engine 20 in one example is a high-bypass geared aircraft engine.The bypass ratio is the amount of air delivered into bypass path Bdivided by the amount of air into core path C. In a further example, theengine 20 bypass ratio is greater than about six (6), with an exampleembodiment being greater than ten (10), the geared architecture 24 is anepicyclic gear train, such as a planetary gear system or other gearsystem, with a gear reduction ratio of greater than about 2.3 and thefan/gear drive turbine section 26 has a pressure ratio that is greaterthan about 5. In one disclosed embodiment, the engine 20 bypass ratio isgreater than about ten (10:1), the fan diameter is significantly largerthan that of the low pressure compressor section 30, and the fan/geardrive turbine section 26 has a pressure ratio that is greater than about5:1. In some embodiments, the high pressure turbine section 40 may havetwo or fewer stages. In contrast, the fan/gear drive turbine section 26,in some embodiments, has between 3 and 6 stages. Further the fan/geardrive turbine section 26 pressure ratio is total pressure measured priorto inlet of fan/gear drive turbine section 26 as related to the totalpressure at the outlet of the fan/gear drive turbine section 26 prior toan exhaust nozzle. The geared architecture 24 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.5:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (“TSFC”). TSFC is the industry standardparameter of the rate of lbm of fuel being burned per hour divided bylbf of thrust the engine produces at that flight condition. “Low fanpressure ratio” is the ratio of total pressure across the fan bladealone, before the fan exit guide vanes. The low fan pressure ratio asdisclosed herein according to one non-limiting embodiment is less thanabout 1.45. “Low corrected fan tip speed” is the actual fan tip speed inft/sec divided by an industry standard temperature correction of [(RamAir Temperature deg R)/518.7)̂0.5]. The “Low corrected fan tip speed” asdisclosed herein according to one non-limiting embodiment is less thanabout 1150 ft/second. Further, the fan 22 may have 26 or fewer blades.

Engines made with the disclosed architecture, and including turbinesections as set forth in this application, and with modifications comingfrom the scope of the claims in this application, thus provide very highefficient operation, and increased fuel efficiency and lightweightrelative to their trust capability.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

What is claimed is:
 1. A gas turbine engine comprising: a fan rotor, afirst compressor rotor and a second compressor rotor, said secondcompressor rotor compressing air to a higher pressure than said firstcompressor rotor; a first turbine rotor, said first turbine rotordriving said second compressor rotor, and a second turbine rotor, saidsecond turbine driving said first compressor rotor; a fan drive turbinepositioned downstream of said second turbine rotor, said fan driveturbine driving said fan through a gear reduction; and said firstcompressor rotor and said second turbine rotor rotating as anintermediate speed spool, and said second compressor rotor and saidfirst turbine rotor rotating together as a high speed spool, with saidhigh speed spool rotating in an opposed direction to said intermediatespeed spool, and said fan drive turbine rotating in the same directionas said intermediate speed spool.
 2. The engine as set forth in claim 1,wherein said fan rotor is driven by said gear reduction to rotate in thesame direction as said high speed spool.
 3. The engine as set forth inclaim 1, wherein a power density of the engine is greater than or equalto about 1.5 lbs/in³, and less than or equal to about 5.5 lbf/in³. 4.The engine as set forth in claim 3, wherein said power density isdefined as a ratio of thrust produced by said engine expressed in poundsforce to a volume of a turbine section incorporating each of said firstturbine rotor, said second turbine rotor and said fan drive turbinerotor, expressed in cubic inches.
 5. The engine as set forth in claim 4,wherein said ratio is greater than or equal to 2.0.
 6. The engine as setforth in claim 5, wherein said ratio is greater than or equal to about4.0.
 7. The engine as set forth in claim 6, wherein said thrust is sealevel take-off flat-rated static thrust.
 8. The engine as set forth inclaim 7, wherein said fan delivering a portion of air into a bypass ductand a portion of air into said first compressor rotor as core flow. 9.The engine as set forth in claim 8, wherein a mid-turbine frame ispositioned between said first and second turbine rotors.
 10. The engineas set forth in claim 9, wherein a turning vane is positioned betweensaid mid-turbine frame and said second turbine rotor.
 11. The engine asset forth in claim 10, wherein a vane is positioned between said secondturbine rotor and said fan drive turbine.
 12. The engine as set forth inclaim 8, wherein a vane is positioned between said second turbine rotorand said fan drive turbine.
 13. The engine as set forth in claim 1,wherein a mid-turbine frame is positioned between said first and secondturbine rotors.
 14. The engine as set forth in claim 13, wherein aturning vane is positioned between said mid-turbine frame and saidsecond turbine rotor.
 15. The engine as set forth in claim 14, wherein avane is positioned between said second turbine rotor and said fan driveturbine.
 16. The engine as set forth in claim 1, wherein a vane ispositioned between said second turbine rotor and said fan drive turbine.17. A gas turbine engine comprising: a fan rotor, a first compressorrotor and a second compressor rotor, said second compressor rotorcompressing air to a higher pressure than said first compressor rotor; afirst turbine rotor, said first turbine rotor driving said secondcompressor rotor, and a second turbine rotor, said second turbinedriving said first compressor rotor; a fan drive turbine positioneddownstream of said second turbine rotor, said fan drive turbine drivingsaid fan through a gear reduction; said first compressor rotor and saidsecond turbine rotor rotating as an intermediate speed spool, and saidsecond compressor rotor and said first turbine rotor rotating togetheras a high speed spool, with said high speed spool rotating in an opposeddirection to said intermediate speed spool, and said fan drive turbinerotating in the same direction as said intermediate speed spool; saidfan rotor being driven by said speed reduction to rotate in the samedirection as said high speed spool; a power density of the engine beinggreater than or equal to about 1.5 lbf/in³, and less than or equal toabout 5.5 lbf/in³; and said power density defined as a ratio of thrustproduced by said engine expressed in pounds force to a volume of aturbine section incorporating each of said first turbine rotor, saidsecond turbine rotor and said fan driving turbine rotor, expressed incubic inches.
 18. The engine as set forth in claim 17, wherein saidratio is greater than or equal to 2.0.
 19. The engine as set forth inclaim 18, wherein said ratio is greater than or equal to about 4.0. 20.The engine as set forth in claim 19, wherein said thrust is sea leveltake-off flat-rated static thrust.